Sapphire Inside: Apple Builds Sapphire Lens into New Home Button, Touch ID

iPhone 5S with the Touch ID includes a sapphire lens

iPhone 5S with the Touch ID includes a sapphire lens on the home button

Today, Apple announced two new models of the iPhone, the iPhone 5S and  the iPhone 5C. One of the biggest news items at the Apple event is that the new iPhone 5S will sport a whole new home button with a fingerprint sensor with a sapphire lens, ringed in stainless steel.

Sapphire, the second hardest material on Earth after the diamond, is scratch resistant, so it should be very well suited for use as a lens. While this is great news for the sapphire community, this is not the only use for sapphire in a smart phone. Many smart phone OEMs already use sapphire for the camera lens cover because of its scratch resistance, but also is used for the LEDs in the backlighting for the screens as well as the silicon-on-sapphire (SOS)-based RFIC chips that power the RF antennas. There are more places for use of sapphire in a smart phone as well since OEMS are looking to use SOS chips for digitally tunable capacitors (DTCs) and power amplifiers. And, don’t forget sapphire’s largest overall market, LEDs, for lighting, displays and more.

Apple claims that Touch ID reads a fingerprint at an entirely new level by scanning sub-epidermal skin layers with 360 degree reading capabilities.  The sensor is part of the home button which is 170 microns thick with a 500 ppi resolution.  Touch ID stores the encrypted fingerprint info securely in a “secure enclave” inside the new A7 chip, the new processor for the iPhone 5S.  The neat thing is that it should be able to store multiple fingers.  The Touch ID will enable you to purchase items on iTunes, the AppStore or iBooks without a password.

You can see where the sapphire is in this photo of the home button from CNet’s live blog of the Apple event:

iPhone 5S graphic illustrates parts of the Touch ID (from CNet)

iPhone 5S graphic illustrates parts of the Touch ID (from CNet) with sapphire








The iPhone 5S (and the 5C) go on pre-sale on September 13th and will be on sale in stores on September 20th.

For Further Reading

Engadget, iPhone 5S fingerprint sensor called Touch ID, recognizes your thumb on the Home button: here’s how it works and what it does,


LTE and the Benefits of Silicon-on-Sapphire

Apple’s iPhone 5 is driving LTE use in the US.

LTE, the next generation wireless communications standard, is making headlines as adoption of mobile devices using LTE picks up.  Deloitte expects nearly 200 million subscribers to migrate to LTE devices by the end of 2013.  Silicon-on-sapphire is playing an important role in the development of devices that operate using LTE.  Peregrine Semiconductor’s Rodd Novack outlined the benefits of silicon-on-sapphire in a recent article in Compound Semiconductor Magazine.

According to Novack, LTE brings technological challenges that impact the RF front end (RFFE) components in wireless devices such as power amplifiers, filters, antennas and switches.  Silicon-on-sapphire, a specific type of silicon-on-insulator (SOI) technology, offers RFFE components scalable integration, consistent performance and the benefits of CMOS, the most widely used semiconductor technology. Silicon-on-sapphire wafers consist of the formation of a thin layer of silicon on a sapphire wafer at high temperature.  Novack says that sapphire, a near perfect insulator, eliminates nearly all of the parasitic capacitance and leakage currents.

The main challenge for the RFFE components is higher linearity.  Sapphire, as an insulating substrate, provides better isolation between circuit elements. In contrast, silicon by itself requires a capacitor to be charged and discharged with every cycle, meaning silicon behaves in a non-linear manner.  However, sapphire provides the linearity LTE needs with its insulator properties.

The RF interference is an important issue with LTE as worldwide deployment is scattered among a range of frequency bands from 699 MHz to 2690 MHz.  This is further compounded by multiple radios in today’s handsets.  As a result, users experience slower data rates and increased dropped calls.  LTE’s linearity performance requirements demand increasingly complex antenna switches which silicon-on-sapphire accommodates easily.

Sapphire improves transistor performance as well as enables high isolation between circuit elements allowing digital and analog blocks to sit next to high-power RF signals according to Novack.  It also enables integration of RF, analog, passive and digital circuitry on one die.  This enables smaller and smaller die and fewer external components.  Novack notes that a smaller switch size is “highly valued, because it can lead to a smaller overall RFFE with greater design and layout flexibility, and fewer external components.”  Eventually, it is thought that silicon on sapphire will enable to System on a Chip (SOC) configurations for smart phones and other electronic devices.

Focus on LTE

LTE (Long Term Evolution or 4G) is the next generation in wireless network technology and successor to 3G.  LTE is significant because it will provide significantly faster data rates for both uploading and downloading for mobile devices.

LTE is seen as the next advance in wireless networks as smart phones, tablets and other wireless devices require more bandwidth for faster data and content downloads. Smart phones, like the iPhone 5, are expected to drive the adoption of LTE.

For Further Reading

Compound Semiconductor Magazine, Silicon-On-Sapphire; Rising Value In Next-Generation Wireless Networks,;-rising-value-in-next-generation-wireless-network.html

Deloitte, A strong year for LTE adoption, (link to article and video)

Peregrine Semiconductor, The History of Silicon-on-Sapphire,

Rubicon Ships 400,000th Large Diameter Sapphire Wafer

Two-inch, Four-inch and Six-inch Sapphire Wafers

Today, Rubicon Technology, Inc. (NASDAQ:RBCN) announced that they shipped their 400,000th six-inch large sapphire wafer to the LED manufacturing and SoS/RFIC markets. Most of the world’s LED manufacturing takes place using sapphire – just as computer chip makers like Intel and AMD use silicon to make their microprocessors.

The most flashy, if you’ll pardon the pun, market for sapphire wafers is in LEDs, which are used for energy-efficient general lighting and as the source for backlighting in consumer products such as HDTVs, laptops, smart phones and tablets.  A second and significantly growing market for sapphire is its use in Silicon-on-Sapphire (SoS) Radio Frequency Integrated Circuits (RFICs).  SoS RFIC chips deliver high RF performance with low power consumption, a small form factor, and significantly reduced crosstalk in antenna applications that are pervasive in smart phones and other consumer devices.

Why large diameter wafers? Rubicon began developing large diameter sapphire wafers for SoS RFICs in the 2000s.  But the company soon tapped into the larger opportunity in the LED market, especially with LED-based general lighting. And, it’s all about the math.

The market has been dominated by two-inch wafers for years. The surface area of a six-inch wafer is nine times greater than that of a two-inch wafer, and its outer curvature is less, enabling greater use of the surface area, culminating in a reduction in edge loss.  In addition, use of larger wafers enables operational savings that offset the cost of the larger, thicker substrate and can help drive down the total cost of LEDs.  According to Rubicon, and depending on the type of MOCVD reactor used, LED chip manufacturers using six-inch wafer platforms may achieve up to 48% greater usable area per reactor run compared with two-inch wafers.

What does that mean? Larger diameter wafers will help LED manufacturers reduce costs throughout the manufacturing process in order to make LED-based lighting more affordable for consumers and encourage adoption worldwide.

Further Reading

Rubicon Technology, Rubicon Technology Ships 400,000th Large Diameter Sapphire Wafer; Company Continues Market Leadership Supplying Large Diameter Sapphire Wafers to LED and SoS/RFIC Markets,

Emerging Markets for Sapphire, Part 1 — SoS

SoS improves performance and integration for RF circuits found in smart phones.

While LED is the largest market for sapphire, there are several other emerging markets that take advantage of the physical attributes of sapphire.  We’ll take a look at these emerging markets over the next month or so.   We will begin with Silicon on Sapphire (SoS) for the RFIC market.

SoS is a part of the Silicon on Insulator (SOI) family of CMOS (Complementary metal–oxide–semiconductor) technology for making integrated circuits.  SoS improves performance and integration for RF circuits.  The holy grail of the wireless industry has been finding a better way to optimize power consumption and real estate utilization in mobile phones.  One application for SoS technology is the production of RF chips used in the antenna switch in smart phones.  These SoS chips are significantly smaller and use less power than chips traditionally used for this application.  As a result, chips produced using SoS technology are rapidly gaining market share in the mobile phone industry.

Peregrine Semiconductor is a pioneer in SoS and holds much of the industry’s IP in SoS.  In an interview with EE Times in 2011, Dr. Ronald E. Reedy, Peregrine co-founder said, “SoS is the first and most successful form of SOI focused entirely on improving performance and integration for RF circuits. We saw the emerging need for such a technology when commercial wireless communications started taking off in the early 1990s.”

What makes sapphire so good for SoS? Peregrine summarized it in a paper on the history on SoS. Sapphire and silicon have a unique way of lining up together at an atomic level because of oxygen atoms.  The scientific explanation is that the r-plane of sapphire has oxygen atoms spaced at a distance that is close to the spacing of the atoms in the (100) plane of a silicon crystal.  The spacing delivers unique insulating properties when the silicon is layered on top of the sapphire wafer.  This was discovered by researchers at Boeing in 1963.  Researchers at RCA continued the development of SoS technology into the mid-1970s and continue to process them for space applications.

Technological barriers leading to defects held SoS back from commercial applications until just recently.  Peregrine has been able to overcome these hurdles at just the right time as the wireless industry needs the insulating and power saving benefits of SoS for the latest generations of smart phones.  You’ll find more coverage of the emerging market in posts to come.

For Further Reading:

Electronics Weekly, Peregrine: Single chip phone RF is possible

EE Times, What’s up with silicon on sapphire?,

Peregrine Semiconductor Corporation, The History of Silicon on Sapphire,,